Aug. 23 (UPI) -- Russian opposition leader Alexei Navalny was released from a Moscow jail Friday, 30 days after being locked up for urging the public to join an unsanctioned protest.

"I have no doubt that despite genuine acts of intimidation and terror that are happening now as random people are being arrested that this wave [of protests] will increase and this regime will seriously regret what it has done," Navalny told reporters outside the Moscow detention center.

Navalny was sentenced late July to 30 days in prison for urging the public to join an unsanctioned protest against the government's decision to prohibit opposition candidates from running for election in the 45-seat Moscow City Duma Parliament, which is controlled by the Pro-Putin United Russia party.

Thousands of supporters who've demanded Navalny and others like him to be added to the ballots for the Sept. 8 election have been rounded up and arrested while other opposition politicians have been detained, subjected to their homes being searched and harassed.

"It is impossible to intimidate us," he said after his release on Instagram. "We despise the cowardly and thieving authorities, which previously had to lie and falsify in order to 'win' the elections, but now they can't do without arrests of candidates, beatings of peaceful protesters and searches, more like robberies."

He said United Russia does not have the support of the people and that he hopes the election will prove that.